Typically, a hairdressing device is used to produce various kinds of hair styles. There are many different kinds of hairdressing devices, including a hair drier for getting a hair dried, a hair curler for waving a hair and a device for straightening a hair. Most of these hairdressing devices are operated by electric power.
The present invention is directed to a hairdressing device for straightening a hair, i.e., for applying a straight permanent to the hair. One example of such hairdressing device is illustrated in FIG. 1.
Referring to FIG. 1, a conventional hairdressing device for applying a straight permanent to a hair is formed of first and second arms 10-1 and 10-2, both of which include a pair of grip portions 4-1 and 4-2, a pair of head portions 8-1 and 8-2 extending from the grip portions 4-1 and 4-2 and a pair of heat generating bodies 6-1 and 6-2 attached to the inner surfaces of the head portions 8-1 and 8-2.
The first and second arms 10-1 and 10-2 are coupled together at their one ends by means of a hinge 12 so that they can be rotated about a hinged point when an external force is applied to the grip portions 4-1 and 4-2.
The heat generating bodies 6-1 and 6-2 are of a planar shape and are heated by electric power. Upon pressing the grip portions 4-1 and 4-2 together, the heat generating bodies 6-1 and 6-2 come into contact with each other. The hair is straightened if the hairdressing device is pulled along the hair nipped between the heat generating bodies 6-1 and 6-2.
The hairdressing device noted above may be used in performing a straight permanent by which a hair such as a curly hair or the like is straightened. When performing the straight permanent, a liquid permanent solution is first applied to the hair to neutralize the same. If the hair is neutralized and if it is the time to perform a straight permanent, the heat generating bodies 6-1 and 6-2 are heated up to a specified temperature by supplying an electric current to the hairdressing device.
Once the heat generating bodies 6-1 and 6-2 reach the specified temperature, a user holds the grip portions 4-1 and 4-2 of the hairdressing device with one hand and pulls the hair away from the head with the other hand. Then, the hair is positioned between the heat generating bodies 6-1 and 6-2 of the head portions 8-1 and 8-2 which are kept spread apart.
Subsequently, the hairdressing device is moved along the hair while pressing the grip portions 4-1 and 4-2 together. As a result, the hair is ironed out into a straight shape by the heat generating bodies 6-1, thereby terminating a straight permanent.
After the straight permanent has been completed, a curing agent is applied to the hair to prolong the duration of the straight permanent. Unlike a typical wave permanent, the straight permanent endures for about six months.
In the straight permanent performed as above, it is important to accurately determine the degree of neutralization of the hair prior to performing the straight permanent. This is because the hair may suffer from severe damage if the permanent is performed in an improperly neutralized state.
In case a straight permanent is performed by a conventional hairdressing device, the degree of neutralization of a hair is empirically determined by pulling the hair after a specified period of time has lapsed from the time of application of a liquid permanent solution. This means that a beginner may encounter a difficulty in accurately determining the point of time for performing the permanent, which is problematic in that the hair may be severely damaged by inaccurate determination of the point of time for performing the permanent. Particularly, in case of an artificial hair, there is a problem in that the permanent effect may easily disappear if the degree of neutralization is improper.